A deadly cocktail of low-intensity explosives and kerosene bombs were used to trigger the blasts in the Delhi-Attari special train, which claimed the lives of 65 passengers, preliminary investigations have revealed.

Forensic experts who collected samples from the scene of blasts were of the view that low-intensity explosives like sulphur or nitrate were used to trigger the explosions and kerosene-filled bottles kept in the bogies were used as a catalyst to spread the fire.

The experts have recovered several kerosene bottles, 3 pipe bombs and some low-intensity explosive devices from other compartments of the train, which caught fire at midnight.

"The modus operandi is new. They had used low-intensity explosives to trigger the blast and kerosene to ignite the fire. The idea it seems was to cause large-scale destruction by fire," J S Mahanwal, Director Forensic laboratory Haryana, said.

Forensic experts said they are yet to find out whether a timer device or some other equipment like flash were used to trigger the explosives.

"We have collected samples and will soon find out how the explosives were triggered," Mahanwal said.

Initial investigations also ruled out use of RDX in the explosions and are moving on the assumption that sulphur or nitrate was used.

"We have defused two pipe bombs, 2 IEDs and recovered 10 to 15 kerosene bottles from three compartments," Mahanwal said.

The experts said igniting fire in a moving train can cause large-scale destruction as was evident from the Godhra episode in Gujarat. The tragedy has also raised questions on the security at the Old Delhi railway station, as the explosives were believed to have been planted at the starting point of the journey.

"It is no doubt a terror attack," Mahanwal said.

Home Minister Shivraj Patil who visited this sleepy town in Haryana also told media persons that some kind of explosives were used to carry out the attack.

A National Security Guard bomb disposal team, headed by Director General Jyoti Kumar Dutt, also inspected the blasts site and collected evidence.